fix(drone): added cache between tests

.drone.yml

@@ -12,21 +12,33 @@ steps:
     image: python
     commands:
       - pip install -r requirements.txt
+    volumes:
+      - name: pip_cache
+        path: /root/.cache/pip
 
   - name: Lint - pylint
     image: python
     commands:
       - pylint wsgi.py app/*.py
+    volumes:
+      - name: pip_cache
+        path: /root/.cache/pip
   
   - name: Lint - flake8
     image: python
     commands:
       - flake8 wsgi.py app/*.py
+    volumes:
+      - name: pip_cache
+        path: /root/.cache/pip
 
   - name: Security analysis with bandit
     image: python
     commands:
       - bandit -r app/
+    volumes:
+      - name: pip_cache
+        path: /root/.cache/pip
  
   - name: Publish the image
     image: plugins/docker
@@ -40,4 +52,9 @@ steps:
       auto_tag: true
     when:
       branch:
-        - master
+        - master
+
+volumes:
+  - name: pip_cache
+    host:
+      path: /tmp/drone/cache/pip_cache